The invention relates to a curable composition comprising a polyvinyl alcohol and a salt of a heterocyclic amino acid Further, the present disclosure relates to an article made from a cured composition comprising a polyvinyl alcohol and a salt of an heterocyclic amino acid. In addition, the present disclosure relates to a method of making the cured composition and the article.
As energy costs rise, membrane technology for separating gases plays an important role in reducing the environmental impact and costs of industrial processes. Gas separation membranes offer a number of benefits over other gas separation technologies. Conventional technologies such as the cryogenic distillation of air, condensation to remove condensable organic vapors from gas mixtures, and amine absorption to remove acid gases such as carbon dioxide from natural gas require a gas-to-liquid phase change in the gas mixture that is to be separated. The phase change adds a significant energy cost to the separation cost. Membrane gas separation, on the other hand, does not require such a phase change.
In addition, gas separation membrane units are smaller than other types of plants, like amine stripping plants, and therefore have relatively small footprints. A small footprint is important in environments such as offshore gas-processing platforms. The lack of mechanical complexity in membrane systems is another advantage.
Currently, gas separation membranes are widely used in industry for hydrogen separation, for example, hydrogen/nitrogen separation in ammonia plants and hydrogen/hydrocarbon separations in petrochemical applications. Other industrial gas separation techniques include separating nitrogen from air; CO2 and water removal from natural gas; and the removal of organic vapors from air and/or nitrogen streams. The most widely used membrane materials for gas separation are polymeric materials, which are especially useful as membranes because of their relatively low cost and ease of processing.
The efficiency of a gas separation membrane process is largely determined by the transport properties of the membrane such as permeability and selectivity for a specific gas in a mixture. Ideally, membranes should exhibit high selectivity and high permeability. For most membranes, however, selectivity and permeability are inversely related. Thus as selectivity increases, permeability decreases, and vice versa.
Rigid polymeric materials may be used for membranes capable of CO2 removal from natural gas streams and in certain instances have shown high selectivity due to a high CO2 diffusive selectivity. A key limitation of many such membranes is that, in the presence of high partial pressures of CO2 or higher hydrocarbon contaminants, the separation properties of the membrane can deteriorate to levels that are not useful. In addition, higher aliphatic hydrocarbons and aromatic hydrocarbons, which are present in small amounts in natural gas, are highly soluble in the polymeric membrane materials employed and can concentrate in and plasticize the polymeric membrane material thereby reducing the diffusive selectivity of the membrane. Because membrane separation properties may be affected negatively by the presence of relatively low levels of impurities in the principal gases undergoing the gas separation process, rigorous and expensive pretreatments may be required.
Therefore, further improvements in membrane performance and properties of gas separation membranes and the corresponding polymeric compositions comprising them are needed. In particular, further improvements are needed to provide polymer compositions which are readily configured as membranes, and which exhibit good performance stability under gas separation conditions, and which exhibit high selectivity for and high permeability to one or more industrially relevant gases. The present invention provides additional solutions to these and other challenges associated with gas separations.